Unit 10: Biological Molecules and Metabolic Pathways Learning Aim A: Understand the structure and function of biological molecules and their importance in maintaining biochemical processes. This assignment and unit was graded an overall DISTINCTION. It is an extremely detailed assignment that meets...
What are biological molecules?
● A biological molecule, also known as a biomolecule, includes large macromolecules
such as lipids, carbohydrates, proteins and nucleic acids as well as small molecules
like hormones and vitamins. These are molecules that are found in organisms that
are needed in one or more than one biological processes such as cell division.
Water
Importance of water
● Water is a vital biological molecule that protects cells, lubricates joints, transports
nutrients and oxygen throughout the body, and aids in controlling body temperature.
In addition, it serves as a catalyst for chemical processes like hydrolysis and a
solvent to dissolve nutrients and minerals.
Structure and bonding of water
● The molecular formula for water is H₂O, it consists of 2 hydrogen atoms and 1
oxygen atom. The molecule is held together by covalent bonds where the hydrogen
atoms share electrons with the oxygen atom. A water molecule is bent in structure
because the oxygen atom forms bonds with hydrogen atoms but it also carries 2 lone
pairs. The water molecule has a tetrahedral shape because the lone pairs repel more
than the bond electrons. The one oxygen atom has a higher electronegativity than
the 2 hydrogen atoms, this means that the oxygen atom attracts the shared electrons
more forcefully. This creates a small dipole moment in the molecule which makes the
oxygen end of the molecule to have a partial negative charge and the hydrogen end
to have a more partial positive charge. This weak attraction between the partial
positive hydrogen and the electronegative oxygen is what causes the hydrogen
bonds. Water is identified as a polar molecule because of its polar covalent bonds
and its bent shape.
Properties of water
● Universal solvent
Water is considered a universal solvent because it is able to dissolve more substances than
any other liquid, but it isn’t capable of dissolving all substances such as fats because of the
low solubility of oppositely charged particles. The reason why water is a universal solvent is
that water molecules consist of a polar arrangement of hydrogen and oxygen atoms. The
hydrogen atom that is found on one side has a positive charge while the oxygen atom on the
other side carries a negative charge. These charges help the water molecule bond to
different types of molecules hence why it is able to dissolve substances.
, ● Hydrogen bonding
Hydrogen bonds are formed when hydrogen atoms form a covalent bond with a very
electronegative oxygen. Water molecules are very polarised molecules this means that they
are able to form many hydrogen bonds. The polar covalent bond between oxygen and
hydrogen creates positive and negative partial charges, there is a weak intermolecular force
of attraction between the partially positively charged hydrogen atoms of one molecule and
the partially negatively charged oxygen atom of another molecule. Since the hydrogen bonds
occur in a straight line (O–H), the covalent bonds of both molecules also occur in a straight
line.
● pH balance
The pH scale is used to determine the concentration of hydrogen ions in water, water has a
neutral pH of 7 which means that it isn't acidic or basic. This is because the concentration of
the hydroxide ion and the hydrogen ions are equal in water making it neutral.
● High specific heat capacity (SHC)
The amount of heat energy (J) required to increase a substance's temperature by 1°C per
kilogramme is known as its specific heat capacity. Water has a high specific heat capacity
because raising its temperature requires more energy. Hydrogen bonding is the reason
behind this. Water molecules and hydrogen bonds can move freely when heat is absorbed.
The hydrogen bonds create and release a large quantity of energy when the temperature
drops. Water has a specific heat capacity of 4,200 J/kg°C. This indicates that 4,200 J are
needed to increase 1 kilogramme of water's temperature by 1°C.
Carbohydrate
Importance of carbohydrates
● Carbohydrates are found in sugars, vegetables, fibres, fruits and legumes. They are
used as energy sources by helping control blood glucose and insulin metabolism as
well as cholesterol and triglyceride metabolism. Carbohydrates have an important
role in the digestive tract as it breaks down carbohydrates into glucose which is
needed for energy consumption.
Structure of carbohydrates
● The atoms carbon, hydrogen, and oxygen make
up carbohydrates, which are big macromolecules.
The formula for carbohydrates is CH₂On. They
are made up of hydroxyl, aldehyde/ketone, and
carbon chains. One oxygen atom is bound to
each carbon atom. Monosaccharides are the
constituent components that make up lengthy
chains of carbohydrates that can be straight or
branched. Three types exist for carbohydrates:
Categories of carbohydrates:
1. Monosaccharides
These are simple sugars. They are used to store and produce energy. They have the
general formula CnH2nOn Examples include: glucose, fructose and galactose.
2. Disaccharides
These are compound sugars that contain two monosaccharides joined together by a
condensation reaction. They are used as an energy source for the body. Examples include:
sucrose, lactose and maltose
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